The IL-36 receptor pathway regulates Aspergillus fumigatus-induced Th1 and Th17 responses

IL-1 drives Th responses, particularly Th17, in host defense. Sharing the same co-receptor, the IL-1 family member IL-36 exhibits properties similar to those of IL-1. In the present study, we investigated the role of IL-36 in Aspergillus fumigatus-induced human Th responses. We observed that different morphological forms of A. fumigatus variably increase steady-state mRNA of IL-36 subfamily members. IL-36α is not significantly induced by any morphological form of Aspergillus. Most strikingly, IL-36γ is significantly induced by live A. fumigatus conidia and heat-killed hyphae, whereas IL-36RA (IL-36 receptor antagonist) is significantly induced by heat-killed conidia, hyphae, and live conidia. We also observed that IL-36γ expression is dependent on the Dectin-1/Syk and TLR4 signaling pathway. In contrast, TLR2 and CR3 inhibit IL-36γ expression. The biological relevance of IL-36 induction by Aspergillus is demonstrated by experiments showing that inhibition of the IL-36 receptor by IL-36RA reduces Aspergillus-induced IL-17 and IFN-γ. These data describe that IL-36-dependent signals are a novel cytokine pathway that regulates Th responses induced by A. fumigatus, and demonstrate a role for TLR4 and Dectin-1 in the induction of IL-36γ.